Portable electrocardiogram (ECG) monitoring and recording devices for use by persons in out-patient (e.g., home or work) environments have long been known Recently, compact devices have been developed that may be worn or carried by a user for monitoring and recording ECG data and transmitting the recorded data through a telephone handset to analyzing equipment at a doctor's office or centralized location. These devices each provide certain benefits, but also suffer from various short-comings and deficiencies. These deficiencies relate primarily to either the physical size of the units or to the way in which the user is required to make contact with the electrodes and subsequently activate the recording sequence.
For example, with some of these known devices the user is required to apply the device (particularly its electrodes) to a body portion (e.g., bare chest) as soon as possible after the on-set of episodic symptoms, such as an arrhythmia. Of course, given the practical delays in finding the unit, locating a private place in which to effect the recording, opening or removing a chest-covering shirt or blouse, applying the unit to the chest and pushing the record button, transient episodic symptoms are often missed.
Other devices have attempted to overcome these "missed-event" deficiencies by requiring the user to apply two or more paste-on electrodes to their body, which electrodes are wired into the device. The unit is worn attached to the user's clothing and a memory loop feature is employed which allows the user ample time to activate the recording sequence after the on-set of episodic symptoms. Since the user actually wears attached electrodes, continuous monitoring is possible and the memory loop ensures that transient ECG data is rarely missed. Patients, however, are generally resistent to wearing either paste-on electrodes or a bulky device attached to their clothing. The paste-on electrodes become uncomfortable over extended periods of time, and the size and placement of the unit on the outside of clothing draws unwanted attention to the patient's medical condition.
U.S. Pat. No. 4,120,294 (Wolfe) discloses a wrist-worn device for monitoring electrical heart signals (e.g., heartbeat rate or ECG), but does not include memory for recording such data. Moreover, the Wolfe unit has only two electrodes--no ground electrode is contemplated--and, therefore, is highly susceptible to muscle artifact signals which can degrade the quality of ECG data pickup. Consequently, even if memory was provided, recording of medical-grade ECG data by such a unit would be unlikely.